Linking to photos in another forum or site often can be confusing. I upload almost all of my photos to Flickr, then link to them from Wander the West or other forums. There are at least two options for linking to photos. One is really easy, and the other is a bit more hammer and chisel (which for some reason is the method I seem to prefer).
So the easy method is to click on the arrow outline when you have the photo brought up in Flickr. It's the outlined arrow in the right bottom of the image. You can click on any of the images here to see a larger version.
Screen Shot 2015-12-02 at 8.21.23 AM.png 247.55K 24 downloads
That brings up a dialog box where you can select the size of the image you want to display, plus how you want to share it. Select and copy the "BBC Code". I like a medium size.
Screen Shot 2015-12-02 at 8.24.21 AM.png 69.93K 13 downloads
You can then simply paste the BBC into your comment. Here's a thumbnail size photo where I did just that. The readers of the comment can click on the image and see it full size on Flickr.
Northern_Harrier_DSC0224 by Stephen Parsons, on Flickr
The hammer and chisel method is a tiny bit more complicated, but does not leave a link back to Flickr. It simply displays the photo. In the screen shot below, there is a down arrow, pointing to a horizontal line.
Screen Shot 2015-12-02 at 8.21.23 AM.png 247.55K 24 downloads
Click on that, then select "View All Sizes"
Screen Shot 2015-08-20 at 12.12.42 PM.png 20.32K 13 downloads
You then select the size you want (I like medium sizes), then right click on the selected image and select "Copy Image Address"
Screen Shot 2015-08-20 at 12.13.19 PM.png 75.71K 9 downloads
Back in WTW, click on the photo icon in the edit box It's the little greenish icon in the clip.
Screen Shot 2015-12-02 at 8.40.11 AM.png 11.02K 10 downloads
You then "Paste the image address that you copied earlier into the dialog box that pops up.
Screen Shot 2015-12-02 at 8.42.40 AM.png 32.35K 8 downloads
Once you have pasted that address in, and clicked OK, you should see your photo in the comment.
If that's as clear as mud, feel free to send me a PM, and I will try and help.